The present invention relates generally to telephone switching systems, and is specifically concerned with a long distance switching system which is adapted to provide a number of enhanced subscriber services in addition to conventional long distance calling.
The restructuring of the U.S. telephone industry has made it possible for telephone subscribers to obtain long distance calling service from a variety of sources. In addition to exerting downward pressure on long distance rates, this has had the effect of encouraging long distance companies to offer subscribers additional service options that were not available previously. As an example, some long distance companies now offer subscribers the option of placing long distance calls from remote locations by dialing an access number (typically a toll-free 800 number), followed by an authorization code known only to the subscriber. Previously, subscribers wishing to place long distance calls from locations other than their own homes or businesses were required to seek operator assistance in order to make appropriate billing arrangements.
There are a number of additional types of services, such as conference calling, call forwarding, speed dialing, and message storage and forwarding, that would be attractive to many long distance telephone subscribers. To date, however, these services have usually been provided only in connection with private branch exchange (PBX) systems. In this type of system, the number of individual telephone stations involved is ordinarily small enough that enhanced services can be provided without a great deal of additional cost. In addition, since PBX systems are ordinarily not required to carry out billing or cost accounting functions (except in the case of outside calls), the problem of configuring the system in order to bill subscribers for these enhanced services on an itemized basis does not arise.
A number of attempts have been made to provide enhanced PBX-type services through a local telephone exchange serving an entire region or community. Generally, this has involved the installation of add-on equipment at the local exchange in order to provide the desired services to subscribers located in the region served by the exchange. The principal limitation of such systems, however, is that most of the enhanced services available to the subscriber (except for certain programming functions) can be accessed only from the subscriber's own telephone set. This is a result not only of the physical placement of the add-on equipment at the local telephone exchange, but also of the fact that the local exchange relies on the origination of the call on the subscriber's line to identify the subscriber for billing purposes.
In principle, it would be desirable to implement conference calling, call forwarding, speed dialing, message storage and forwarding, and other PBX-type services in a long distance switching environment. This would have the advantage of allowing these enhanced services to be accessed by subscribers located at any point within a wide geographic area. In practice, however, such an extension has not been feasible for at least two reasons. In the first place, the architecture of existing types of switching systems limits the amount and type of information which can be passed through the switch, a situation which makes it difficult to bill subscribers for enhanced services on an itemized basis. The second factor is the possibility that unauthorized callers may gain access to the long distance system, causing economic loss to the company operating the system and disruption to the subscriber. Unauthorized access is already a serious problem in conventional long distance calling, but the potential for abuse is obviously much greater when services other than long distance calling are available to the unauthorized user. The use of individual access codes known only to the subscribers can alleviate the problem to some extent, but this does not provide a complete solution since these codes may, in time, become known to others.